1. Field of Invention
The present invention relates to an electrical junction box suitable to be connected for example to one or more wire harnesses in a vehicle such as an automobile.
2. Description of Related Art
Recently, the increase of electrical and electronic component parts which are mounted in a vehicle has led to increase of circuits to be accommodated in electrical connection boxes and junction boxes in the vehicle. Thus, when forming branch circuits at a high density, it is necessary to mount a large number of component parts on a junction box or the like, which causes increase of manufacturing complexity.
In a junction box disclosed in JP-A-2000-92660 and shown in present FIG. 12, bus bars 5A-5D are laminated one upon another between an upper case part 2 and a lower case part 3, with insulation plates 4A-4E interposed between the bus bars 5A-5D. The upper case part 2 has a connector receiving portion 2a, a relay receiving portion 2b, and a fuse receiving portion 2c, on which in use connectors 6, relays 7 and fuses 8 are mounted respectively. Terminals of the connectors 6, the relays 7 and the fuses 8 are connected to tabs 5a projecting from the bus bars directly or are connected to the bus bars through relaying terminals. The lower case part 3 has also a connector receiving portion 3a to connect connectors to tabs projecting from the bus bars.
In the junction box 1, with the increase of the number of circuits, the area and the number of layers of the bus bars increase and thus the size of the junction box becomes large. If the connector, relay and fuse receiving portions are arranged on both the upper and lower case parts to connect connectors, relays and fuses to internal circuits of the junction box, it is possible to make the area of the junction box smaller than in the case where the receiving portions are mounted on only the upper case part or the lower case part.
However, if the connector, relay and fuse receiving portions are mounted on both the upper and lower case parts such that they are opposed vertically, the bent tabs of bus bars must overlap each other and thus cannot be easily arranged. In this case, it is necessary to form tabs on bus bars of other layers, which causes an increase of number of layers of bus bars, and thus leads to the increase of the height of the junction box. That is, the junction box is necessarily large.
Further, the above-described junction box is so constructed that the bus bars are connected to the connectors, the fuses and the relays. Thus, when the specification of the connection between the internal circuit and the fuses and/or the relays is altered, it is necessary to alter the entire internal circuit. Consequently the above-described junction box is incapable of allowing a circuit alteration easily.
Some proposals have been made for replaceable modules in electrical circuits of automobiles.
U.S. Pat. No. 5,179,503 shows a modular automobile power distribution box having replaceable modules carrying relays or fuses. The relays or fuses in each module are directly connected to terminals of leads of wire harnesses. A pair of bus bars connect power terminals to the fuses of three maxi-fuse modules. There is no discussion of interconnection of the modules.
U.S. Pat. No. 5,581,130 discloses removable multi-function modules in individual casings which are mounted on a circuit board. Each module is electrically connected to the power supply distribution layer of the board by a pin. Alternatively three modules are shown connected together by two electrical and mechanical coupling bars.
It is an object of the present invention to provide a junction box which can be made thin without increasing the number of layers of bus bars to be accommodated therein and which can cope with a circuit alteration easily.
According to the present invention, there is provided an electrical junction box adapted to provide electrical connection to a plurality of electrical connectors, a plurality of fuses and a plurality of relays, having
(i) a casing;
(ii) a connector circuit having at least one connector circuit insulation substrate and a plurality of first bus bars fixed on the insulation substrate, the first bus bars being arranged to provide electrical connection to electrical connectors in use;
(iii) a fuse circuit having at least one fuse circuit insulation substrate, which is discrete from the connector circuit, and a plurality of second bus bars fixed on the fuse circuit insulation substrate, the second bus bars being arranged to provide electrical connection to fuses in use; and
(iv) a relay circuit having at least one relay circuit insulation substrate, which is discrete from the connector circuit, and a plurality of third bus bars fixed on the relay circuit insulation substrate, the third bus bars being arranged to provide electrical connection to relays in use;
(v) wherein at least one of the second bus bars and at least one of the third bus bars are joined to respective ones of the first bus bars by welded connections formed by welding together of respective welding portions of the bus bars projecting from the respective insulation substrates; and
(vi) wherein, at at least one of the welded connections, the junction box is provided with a protection structure which receives the welding portions of the respective bus bars of the welded connection and presses the welding portions towards each other.
Preferably the two welding portions at the welded connection are insertable in a press-fit manner in a recess of the protection structure.
The protection structure provided for the or each welded connections of the bus bars has the function of pressing or clamping the joined welding portions of the respective bus bars, so that the risk of disconnection of the welded connection is reduced or avoided. Preferably the protection structure clamps the welding portions resiliently, thereby reducing the risk that the welding portions are disconnected by vibration or shock forces occurring in use of the junction box. The protection structure is preferably formed of molded plastics material, and as described below may be a portion of the casing of the junction box. In this case, the protection structure is fitted on the welded connection during assembly of the junction box in such a manner that the welded connection is fixedly held in the recess of the protection structure.
The electrical junction box of the present invention has a modular construction. As described above, in the junction box of the present invention, the fuse circuit substrate and the relay circuit substrate are separately provided from the connector circuit substrate and are then joined by welding of the bus bars. This is in contrast, in the conventional method, electrically conductive sheets are punched to form unitarily the connector connection circuit, the fuse connection circuit, and the relay connection circuit and form tabs to be connected to connectors, tabs to be connected to fuses, and tabs to be connected to relays and stacked in a single stack, the circuits thus being handled and arranged in a complicated manner. Consequently, in the conventional method, the area of the bus bars increases and a large number of bus bars are necessary.
On the other hand, in the present invention, because the circuits are separately provided and welded, it is possible to avoid the complication of tabs overlapping each other and avoid a large number of bus bars. Thus, it is possible to form a thin or compact junction box. Further, because the circuits of the bus bars can be handled and arranged easily, the area of each bus bar can be reduced. Consequently, even though the bus bars are separately provided for the connector connections on the one hand and the fuse connections and the relay connections on the other hand, it is possible to reduce the total area of the bus bars and avoid increase of the area of the junction box.
Preferably, the connector module having the connector circuit, the fuse module having the fuse circuit, and the relay module having the relay circuit are all separately provided, i.e., the respective insulation substrates are discrete from each other. Thus, if the specification of any one of the connector circuit, the fuse circuit, and the relay circuit is altered, only the design of any one of the modules need be changed. That is, the construction can cope with the alteration of the specification easily.
The first bus bars are provided separately from the second or/and third bus bars but connected thereto by means of welding. Thus this construction does not reduce reliability of the electrical connections. The welding portions may be connected to each other by ultrasonic welding, resistance welding, laser welding or gas welding. The welding portions connecting the modules to each other are inserted into the protection structure having an accommodation space or recess capable of accommodating the welding portions and are pressed towards each other by a protection portion. Thus, even though the circuits are subjected to vibrations or the like, the welding portions are securely protected and thus prevented from being separated from each other.
It is preferable to form a widening guide portion at an entrance of the recess or accommodation space of the protection structure. This construction allows the welding portions to be guided into the recess easily and securely when covering the welded connection with the protection structure. It is preferable to form the protection structure integrally with a casing, e.g., an upper case part or a lower case part accommodating the connector circuit, the fuse circuit, and the relay circuit. Thereby it is possible to enclose each circuit with the upper and lower case parts and at the same time press the welding portions into the protection structures by press fitting.
Although the fuse circuit and the relay circuit may be separately formed, it is possible to integrate them with each other to form a fuse/relay composite circuit which receives fuses and relays on the same substrate which has bus bars for fuses and relays thereon. In this case, if it is necessary to connect the circuit of any of the bus bars for fuses to any of the bus bars for relays, the respective bus bars may be welded to each other or the bus bars may be integrally formed.